I took up walking some time ago. I started at 1-2 kms and now walk 6-10 kms daily. I enjoy it and do a lot of thinking while walking. The added bonus was losing 17 kgs, which amazed me as that hadn't been the reason I started walking.
Fast walking in a park, or anywhere there're trees & plants, not beside cars breathing in poisonous emissions!
Swimming, too, is excellent, as tones muscles, & uses ALL of the body.
So does horse-riding, but not great on the weight loss part, though! Lol!
Since I wrote my 1st answer, I've lost my iPod charger, so I now don't walk if my friend isn't walking, & I've stacked on 3 kilos! Ops! So now it is a big fat YES, for keeping the weight down! (I now think that's why people walk, jog & run, quiet frankly!)